This invention relates to an apparatus for performing a white balance self-adjustment, which is for use in a color TV display or in a color monitor for a personal computer.
In the field of color TV displays, it is necessary, before putting TV display products to market, to adjust the white balance of each product by setting the DC voltage level and gain of each color signal output of the three primary colors R (Red), G (green) and B (Blue) on the basis of the cut-off characteristics of a color CRT (Cathode Ray Tube) incorporated in the product.
In the prior art, the state of white balance of the product is detected by monitoring the screen of the CRT with a TV camera, etc., then the detected value is fed back to a computer system for adjustment or to an adjusting person, where the value is compared with a preset reference value, and the DC voltage level and the gain of each of the R, G and B color outputs are adjusted on the basis of the comparison result.
In the case of performing the adjustment manually, variable resistors incorporated in a DC voltage level and gain adjusting circuit (hereinafter referred to as a "DC-voltage-level/gain adjusting circuit") for adjusting the DC voltage level and the gain are manually adjusted. On the other hand, in the case of performing the adjustment using the adjusting computer system, adjustment data is supplied to a video signal-processing integrated circuit through a data bus, incorporated therein, to rewrite data therein.
As mentioned above, the above-described prior method requires a TV camera, an adjusting computer system or an adjusting person. Moreover, in the prior method, the white balance characteristics cannot be self-adjusted to compensate aged deterioration of the CRT after the TV display is put to use.
In light of this, the conventional color TV display additionally employs a cathode current detection circuit so as to enable the display to detect a cathode current of the CRT corresponding to a reference signal output from the video signal processing integrated circuit, and employs a method for converting a detected cathode current to a detection value for each of RGB electron guns, then comparing the converted value with a preset reference value, storing the comparison result in a capacitor, and adjusting the DC voltage level and the gain of each of the R, G and B color outputs on the basis of the stored voltage value.
However, although this method enables self-adjustment of white balance to compensate usual aged deterioration of the CRT characteristics, it does not enable the self-adjustment in the manufacturing stage of the display, and further requires an integrated circuit of a large scale since a capacitor of a large capacitance is necessary for storing an analog voltage.
In addition, in the method, the voltage stored in the capacitor is substantially 0 V and therefore the CRT screen intensely flashes in white immediately after the TV display is turned on. To deal with this, a particular countermeasure circuit is necessary.